zhangweiwu@realss.com (2004-04-11 at 2223.38 +0800):

I know the question might be silly, because I can dig it out by RTFM.

RTFPS, P of PNG and S of Spec. But I think GIMP does not support saving indexed images in which the palette items are RGBA instead of RGB. You could have tried, convert to index and see if GIMP keeps all transparent areas or not.

GSR

Hi,

Zhang Weiwu writes:

Thank you Michael Schumacher for helping me on the IE transparent pixel problem last time.

Now I have a question: is it possible to create a png file with indexed color, with transparent pixels, while still have an alpha channel, so that the png file display alpha channel on cool browsers like Mozilla, while display transparent pixels on some inferior browser like IE as a fall-back mechanism? If GIMP cannot do it, can it be done in theory?

I know the question might be silly, because I can dig it out by RTFM. But I just wish a quick answer so I don't have to waste time on impossible things:)

The PNG file format supports it but GIMP can't create such files and I have no idea how IE would render them

From http://www.libpng.org/pub/png/pngintro.html:

But PNG supports alpha information with palette images as well; it's just slightly harder to implement in a smart way. A PNG alpha-palette image is just that: an image whose palette also has alpha information associated with it, not a palette image with a full alpha mask. In other words, each pixel corresponds to an entry in the palette with red, green, blue and alpha components. So if you want to have bright red pixels with four different levels of transparency, you must use four separate palette entries to accommodate them. (All four entries will have identical RGB components, but the alpha values will differ.) If you want all of your colors to have four levels of transparency, you've effectively reduced your total number of available colors from 256 to 64.

Sven

Zhang Weiwu wrote:

Thank you Michael Schumacher for helping me on the IE transparent pixel problem last time.

Now I have a question: is it possible to create a png file with indexed color, with transparent pixels, while still have an alpha channel, so that the png file display alpha channel on cool browsers like Mozilla, while display transparent pixels on some inferior browser like IE as a fall-back mechanism? If GIMP cannot do it, can it be done in theory?

Likely your best solution, although a pain in the posterior, would be to create two images and then use a bit of javascript to present the proper image depending on the browser...